Method and device for controlling an electric actuator activating a functional system

ABSTRACT

This device comprising a control member ( 2 ) actuatable by a user so as to govern the powering of the actuator, is characterized in that it comprises means ( 10 ) for estimating the movements of the control member ( 2 ), along a travel thereof between extreme positions of control of the actuator, and means ( 12, 13, 14, 15, 16 ) for analysing these movements so as to derive therefrom a cue for controlling means ( 17 ) for powering the actuator so as to supply the latter with a quantity of current corresponding to the movement of the control member, as determined by these means of analysis on the basis of a predetermined correspondence law ( 15 ) stored in the latter means and of means ( 16 ) for aggregating the successive movements of the actuator during its various controls, and updated after each new control of the actuator by these means of analysis, so as to slave the position of the actuator to the position of the control member.

FIELD OF THE INVENTION

The present invention relates to a process and device for controlling anelectric actuator for activating a functional system, comprising acontrol member actuatable by a user so as to govern the powering of theactuator.

BACKGROUND OF THE INVENTION

Such a functional system can be constituted by an automotive vehiclesecondary brake.

Secondary brake devices, that is to say parking brake devices, are knownwherein activation is effected by electric actuators whose operation isgoverned by a user by way of a control member making it possible todrive the powering of the actuator.

The control member is constituted in such devices in particular by aswitch making it possible to power or otherwise the actuator, that is tosay in fact to bring about complete application or release of thesecondary brake of the vehicle.

Systems of this type also comprise electronic means for managing thepowering of the actuator as a function of cues emanating from sensorsfor example sensing the rate of rotation of the wheels of the vehicle,such as those used in wheel anti-lock systems.

However, such means have a number of drawbacks, especially as regardstheir cost, their operation and their manipulation by a user.

Indeed, one is aware that managing the holding of a vehicle stationaryon a slope is relatively simple to manage with such an interface, by forexample powering the actuator under full voltage.

However, the cue delivered to the device by the user via such aninterface, is of the all or nothing type, whereas by using a traditionalbrake lever for tensioning the cables for applying the secondary brake,the user manages the tension of the cable and its rate of tensioning andregulates the latter as a function of the deceleration of the vehicle.

It is appreciated that for various reasons it is desirable to preservesuch functional capabilities.

The objective of the invention is therefore to solve these problems atminimum cost.

To this end, the subject of the invention is a process for controllingan electric actuator for activating a functional system, especially anautomotive vehicle secondary brake, of the type comprising a controlmember actuatable by a user so as to govern the powering of theactuator, characterized in that it comprises the following steps:

a) the movements of the control member are estimated, in terms ofdirection and amplitude, along a travel thereof between extremepositions of control of the actuator, and

b) these movements are analysed so as to derive therefrom a cue forcontrolling means for powering the actuator so as to supply to thelatter a quantity of current corresponding to the movement of thecontrol member, as determined on the basis of a predeterminedcorrespondence law and of means for aggregating the successive movementsof the actuator during its various controls, and updated after each newcontrol thereof, so as to slave the position of the actuator to theposition of the control member.

According to another aspect, the subject of the invention is also adevice for controlling an electric actuator for activating a functionalsystem, especially an automotive vehicle secondary brake, of the typecomprising a control member actuatable by a user so as to govern thepowering of the actuator, characterized in that it comprises:

a) means for estimating the movements of the control member, in terms ofdirection and amplitude, along a travel thereof between extremepositions of control of the actuator, and

b) means for analysing these movements so as to derive therefrom a cuefor controlling means for powering the actuator so as to supply thelatter with a quantity of current corresponding to the movement of thecontrol member, as determined by these means of analysis on the basis ofa predetermined correspondence law stored in the latter means and ofmeans for aggregating the successive movements of the actuator duringits various controls, and updated after each new control of the actuatorby these means of analysis, so as to slave the position of the actuatorto the position of the control member.

The invention will be better understood with the aid of the descriptionwhich follows, given merely by way of example while referring to theappended drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents a schematic diagram illustrating the installation of adevice for controlling an electric actuator for activating a functionalsystem such as an automotive vehicle secondary brake;

FIG. 2 represents a schematic diagram illustrating the structure and theoperation of such a device;

FIGS. 3 and 4 represent graphs illustrating the determination of thequantity of current.

DETAILED DESCRIPTION

Represented in fact in FIG. 1 is an automotive vehicle designated by thegeneral reference 1, which is equipped with a functional system such asa secondary brake also known in the state of the art as a parking brake.

This functional system comprises a control member actuatable by a user,designated by the general reference 2 and comprising for example alever.

This lever is associated with an electric actuator designated by thegeneral reference 3, making it possible to control the tensioning ofcables, for example 4 and 5, for tensioning the callipers 6 and 7 forbraking the rear wheels of the vehicle.

In fact, the electric actuator 3 can comprise an electric motorassociated with means for winding/unwinding the cables for actuating thesecondary brake of the vehicle.

In a desire to economize with regard to such an actuator, the electricmotor is preferably an electric motor of the direct current type.

In the process and the device according to the invention, one focuses onnot losing the functional capabilities of an automotive vehicleconventional secondary brake, by proposing an interface equivalent tothat currently installed in the vehicles, that is to say which allowsthe user to control the tension of the cable and its rate of tensioningand to regulate this tension as a function of the deceleration of thevehicle, by carrying out a correlation between the position of thecontrol member 2 and the tension of the cables.

In this case, the tension of the cables is regulated by the user byslaving the position of this member to the deceleration of the vehicleas experienced by this user.

To achieve such a mechanism, the simplest and most economical solutionconsists in carrying out slaving between the tension of the cables and acontrol member position cue output by a sensor associated with themember.

However, this involves the use of sensors of the load on the cables,this being a relatively expensive technology.

Now, the price criterion is an important criterion and this slaving musttherefore be achievable without any cable tension sensor.

Therefore the control process and device according to the invention usemeans for powering the actuator with quantities of current calculated asa function of the movements of the lever or control member 2.

To this end, in the control process according to the invention, themovements of the control member 2 are estimated, in terms of directionand amplitude, along a travel thereof between extreme positions ofcontrol of the actuator 3, and these movements are analysed so as toderive therefrom a cue for controlling means for powering the actuatorso as to supply to the latter a quantity of current corresponding to themovement of the control member. This quantity of current T_(p) isdetermined on the basis of a predetermined correspondence law and ofmeans for aggregating the successive movements X of the actuator duringthese various controls, and updated after each new control thereof, soas to slave the position of the actuator to the position of the controlmember.

Thus, a law dependent on the mechanical and electrical characteristicsof the system and of the vehicle is established between the movements ofthe control member 2 and a quantity of current T_(p) to be supplied tothe actuator so as to slave the position of this actuator to theposition of the control member.

With such a system operating in open loop, it may be subject todrifting.

The latter is then compensated for by a gauging of the control forpowering the actuator with each passage to the extreme position of thetravel of the control member.

The inertia of the functional system as well as its frictionalcharacteristics are taken into account by filtering the power suppliedto the actuator.

This filtering dispenses with the despatching of a quantity of currentto the actuator when this quantity is below a predetermined threshold,that is to say is too small to “shift” or activate the motor, but storesand numerically aggregates what has been filtered so as to despatch itto the actuator when the quantity of current is sufficient to activatethe motor.

It is then appreciated that in the case where the actuator comprises anelectric motor associated with means for winding/unwinding a cable foractuating the functional system, the governing strategy describedearlier makes it possible to estimate the winding/unwinding of the cablevia a decomposition of the quantities of current for controlling thismotor.

Indeed, in order to govern the motor, it is appropriate to calculate thequantity of current to be supplied to the motor so as to obtainwinding/unwinding of the cables corresponding to the movement of thecontrol member.

The quantities of current supplied successively to the actuator duringthese various controls are then stored in aggregation means which areupdated after each new control of the actuator, their content being theimage of the state of winding/unwinding of the cables.

The factor making it possible to convert the movements of the controlmember into a quantity of current supplied to the motor is interpolatedas a function of the content of these means of aggregation.

An exemplary embodiment of a device for implementing this process isdescribed in FIG. 2.

Depicted in fact in this figure are the control member designated by thegeneral reference 2 and the electric actuator 3 for activating thefunctional system, this electric actuator comprising for example anelectric motor 8 associated with means for winding/unwinding at leastone cable for actuating the functional system, these means beingdesignated by the general reference 9, whilst the cables are designatedby the general references 4 and 5 and the callipers associated with therear wheels of the vehicle by the references 6 and 7.

The control member 2, that is to say in fact for example the lever, isassociated with a position sensor of conventional type designated by thegeneral reference in this figure, the output of which is associated withgauging means designated by the general reference 11, making it possibleto compensate for the drifting of the system by gauging the control forpowering the actuator with each passage to the extreme position of thetravel of the control member.

Indeed, if the control member is in the position of complete release,the means for powering the actuator are reset to zero, whereas if thecontrol member is in the position of maximum application, the means forpowering the actuator supply the latter with maximum power.

The output of these gauging means is supplied to means for estimatingthe movements of the control member 2, in terms of direction andamplitude, along the travel thereof between its extreme positions, thesemeans of estimation being designated by the general reference 12 in thisfigure.

These means of estimation make it possible to deliver to the remainderof the circuit, cues relating to the direction and amplitude of movementof the control member.

These cues are then analysed by a cues processing unit designated by thegeneral reference 13, comprising for example a calculation unitdesignated by the general reference 14 associated with data storagemeans designated by the general references 15 and 16 in this FIGURE.

The storage means 15 are for example suitable for storing thepredetermined correspondence law, such as described earlier, whilst thestorage means 16 are suitable for storing the quantities of currentsupplied successively to the actuator during its various controls, thesemeans being updated after each new control thereof by the calculationunit 14.

The correspondence law mentioned earlier and the means of aggregationthen allow the calculation means 14 to determine a cue for controllingmeans 17 for powering the actuator, so as to supply the latter withquantities of current in respect of the movements of the actuator andwhose number is determined on the basis of this predeterminedcorrespondence law and of these means of aggregation as was describedearlier.

Finally, it will also be noted that this device comprises means 18 ofdiagnosis of its operation.

These means are for example based on a comparison of the calculatedpowering of the actuator, of the type: calculated motor currentrating=measured battery voltage/resistance of the motor and of itseffective powering, that is to say the measured motor current rating.

It goes without saying of course that other means of diagnosis may beenvisaged.

It is then appreciated that by virtue of such a structure, it ispossible to use a control member which can be moved along a travelbetween extreme positions of control of the actuator and that themovements of this control member are analysed, in terms of direction andamplitude, so as to acquire cues from the user relating to the governingof the actuator.

These cues relating to the movement of the control member are thereafteranalysed so as to determine a cue for controlling the means for poweringthe actuator so as to supply the latter with a quantity of current whichdepends on the estimated movement of the control member.

This determination is carried out by a unit for processing cues on thebasis of a predetermined correspondence law taking into account thevarious characteristics of the functional system needing to be governedand of the means for aggregating the quantities of current suppliedsuccessively to the actuator during these various controls, these meansof aggregation being updated after each new control of the actuator.

The determination of this quantity of current is represented in FIGS. 3and 4 which show graphs respectively illustrating the setting of thecontrol member 2 and the quantity of current necessary T_(p).

The law of correspondence between these two values is of the type:

T_(p)=Δc×Coeff k;

where: T_(p)=quantity of current;

Δc=variation of the position of the lever;

Coeff k=nonlinear variable coefficient making it possible to compensatefor the nonlinearity of the winding, dependent on the movements X of theactuator.

It is understood that this quantity of current T_(p) makes it possibleto move the cable, that is to say to wind it or unwind it by a value X,the latter corresponding to:

X=T_(P)/T elementary;

where T elementary=elementary quantity of current.

The means for aggregating the estimated movements advantageously make itpossible to determine the quantity of current necessary T_(p), thesemeans interfering directly on the value of the coefficient k.

This determination makes it possible to take into account the state ofwinding of the cable, since much more energy and hence a greaterquantity of current is required to wind the cable if the latter isalready mostly wound.

This then makes it possible to slave the position of the actuator to theposition of the control member.

Of course, other means such as for example other forms of control membermay be envisaged.

The actuator, that is to say for example the electric motor and themeans for winding/unwinding the cables, as well as the variouselectronic means associated with the governing thereof may be mountedtogether in a common block supporting the control lever.

Of course, the load experienced by the user when maneuvering this membermay be either linear or modulated by means of variable braking of itsmovement along its travel, these means comprising for example a cam orany other mechanical, electrical or hydraulic member making it possibleto vary the load to be applied by the user to this lever as a functionof its position along its travel.

What is claimed is:
 1. Process for controlling an electric actuatorcomprising: a control member actuatable by a user so as to govern thepowering of the actuator, the process comprising the following steps: a)the movements of the control member are estimated, in terms of directionand amplitude, along a travel thereof between extreme positions ofcontrol of the actuator, control for powering the actuator is gaugedwith each passage to the extreme position of the travel of the controlmember, b) these movements are analyzed so as to derive therefrom a cuefor controlling means for powering the actuator so as to supply to thelatter a quantity of current corresponding to the movement of thecontrol member, as determined on the basis of a predeterminedcorrespondence law and of means for aggregating the successive movementsof the actuator during its various controls, and updated after each newcontrol thereof, so as to slave the position of the actuator to theposition of the control member.
 2. Process according to claim 1, whereinthe quantities of current which are below a predetermined threshold arefiltered and these are aggregated so as to feed them back to theactuator when this aggregate is sufficient to activate the actuator. 3.Device for controlling an electric actuator for activating a functionalsystem, especially an automotive vehicle secondary brake, having acontrol member actuatable by a user so as to govern the powering of theactuator, the device comprising: a) means for estimating the movementsof the control member, in terms of direction and amplitude, along atravel thereof between extreme positions of control of the actuator, andb) means for analyzing these movements so as to derive therefrom a cuefor controlling means for powering the actuator so as to supply thelatter with a quantity of current corresponding to the movement of thecontrol member, as determined by these means of analysis on the basis ofa predetermined correspondence law stored in the latter means and ofmeans for aggregating the successive movements of the actuator duringits various controls, and updated after each new control of the actuatorby these means of analysis, so as to slave the position of the actuatorto the position of the control member; and means for gauging the meansfor controlling the powering of the actuator with each passage to theextreme position of the travel of the control member.
 4. Deviceaccording to claim 3, further comprising means for filtering thequantities of current which are below a predetermined threshold andmeans for aggregating these quantities so as to feed them back to theactuator when this aggregate is sufficient to activate the actuator. 5.Device according to claim 3, wherein the control member furthercomprises a lever.
 6. Device according to claim 5, wherein the means forestimating the movements of the control member comprise a lever positionsensor.
 7. Device according to claim 3, wherein the control member isassociated with means of variable braking of its movement along itstravel.
 8. Device according to claim 7, further comprising means ofdiagnosis of its operation.
 9. Device according to claim 3, wherein theactuator further comprises an electric motor associated with means forwinding/unwinding at least one cable for actuating the functionalsystem.